In an electric driving apparatus, which is applied to an electrical power steering system of a vehicle for assisting a steering operation of a vehicle driver, it is known in the art that an electric motor and a controller for driving and controlling the electric motor are combined into one, for example, as disclosed in Japanese Patent Publication No. 2002-120739.
According to the above controller, the electric motor is operated by a single system of an inverter circuit. Therefore, in a case that the inverter circuit breaks down, a load to the vehicle driver for the steering operation is increased.
In a case that two systems of the inverter circuits are provided for driving the electric motor, it is possible to continuously drive the electric motor by one of the inverter circuits even when the other of the inverter circuits breaks down.
However, when a difference exists between a value of driving current supplied to the electric motor from one of the inverter circuits and a value of driving current supplied to the electric motor from the other of the inverter circuits, a rotational balance of the electric motor becomes worse and driver's feeling for the steering operation may be decreased.